In processing metal parts, the metal or alloy is typically first formed into rods, bars, billets, sheets or plates to be used as a starting material for subsequent processing. Preformed shapes produced by different production methods may also be used for raw material input to subsequent processing. The input material may then be subjected to manufacturing processes such as forging, pressing, stamping, impact forming, spinning, flow turning and/or heat treating. As a preliminary and necessary step to these manufacturing processes, the input material typically must first be heated. Convection ovens are one known method for heating the metal parts for subsequent processing. However, oven heating has disadvantages, such as high net energy input.
Recently, infrared (IR) heating has been proposed as a means for heating parts for subsequent manufacturing operations. Infrared is an “instant on” heat source that uses energy only when needed, resulting in a significantly lower net energy input than convection ovens. Improvements in the microstructure and physical properties of metal parts may also be achieved by the use of IR rapid heating. However, variations in the surface finish on the various surfaces of a metal part or between the surfaces of different metal parts in a batch process will cause the parts or the surfaces thereof to achieve different temperatures at different rates. Such temperature differences will have deleterious metallurgical affects and potentially render the products unacceptable for use.
Dip and spray coatings have been used as a means for applying material to act as a lubricant in subsequent aluminum manufacturing processes. However, these treated aluminum parts will have non-uniform coatings that are not intended to address the surface finish of the part when subsequent processing involves IR radiance as the means for heating the part. Thus, previous attempts to utilize IR heating of aluminum and other metal parts have been unsuccessful due to the lack of control of the surface finish, such as surface reflectivity. Insufficient consideration has been given to the reflection of energy from the metal surface, and the resulting variable heating rates that cause under-temperature and over-temperature conditions in the IR heated parts.
There is thus a need for a method of preparing metal parts for heating by IR radiance that addresses the importance of the surface finish of the metal parts during subsequent metal heating.